The invention relates to a turntable for a disc-shaped information carrier, which turntable is provided with a central element which has a central shaft opening, a support surface for the information carrier extending perpendicularly to a central axis of the shaft opening, and a driving member having an output shaft for rotationally driving the central element and the support surface, which shaft forms a clamping connection with the shaft opening wherein the shaft extends over an insertion length.
The invention also relates to a player for disc-shaped information carriers, which player is provided with a turntable, which turntable is provided with a central element which has a shaft opening, a support surface for the information carrier extending perpendicularly to a central axis of the shaft opening, and a driving member having an output shaft for rotationally driving the central element and the support surface, which shaft forms a clamping connection with the shaft opening wherein the shaft extends over an insertion length.
A turntable and a player of the types mentioned in the opening paragraphs are generally known and generally used, for example in CD players and DVD players. In order to bring about the clamping connection between the shaft and the shaft opening the shaft is pressed into the shaft opening. This causes the problem that due to an almost unavoidable slight misalignment between the central axes of the shaft opening and the shaft when it is pressed, asymmetrical accumulation of material occurs, as a result of which the cylindrical shaft opening is to some extent asymmetrically deformed. This is at the expense of the perpendicularity between the support surface and the output shaft, which in particular at relatively high speeds of rotation, such as for example 200 revolutions per second in a DVD player, can lead to instabilities and oscillation effects, even if said lack of perpendicularity occurs only to a very limited extent. Moreover, state-of-the-art optical players are using laser light with increasingly shorter wavelengths. This also imposes more stringent requirements on the permissible axial excursion of the information carrier during rotation, because of the tolerances concerning the focal distance. In order to achieve the required perpendicularity between the support surface and the output shaft, the central element with the output shaft clamped in the shaft opening is subjected to a machining operation, which is a very costly matter.
An aim of the invention is to provide a turntable and a player of the type mentioned in the opening paragraphs, wherein the abovementioned disadvantage of the known turntable and the known player is overcome as far as possible, and wherein during mass-production a relatively high accuracy in the assembled state in terms of the perpendicularity between the output shaft and the support surface is achieved.
In order to achieve this aim, a turntable in accordance with the invention is characterized in that only a contact portion of the output shaft having a contact length which is smaller than the insertion length is in clamping contact with the shaft opening.
In order to achieve this aim, a player in accordance with the invention is characterized in that the turntable used therein is a turntable in accordance with the invention.
The invention is based on the recognition that it is not necessary to bring the output shaft and the shaft opening into clamping contact with each other over the entire insertion length to achieve a good power transmission between the output shaft and the central element with the support surface coupled thereto. By limiting the contact between the output shaft and the shaft opening to a contact length that is smaller than the insertion length, the amount of deformation that occurs on the surface of the shaft opening or of the output shaft is considerably reduced. There is also space and opportunity for any accumulating of material to xe2x80x9csettlexe2x80x9d within the insertion length but outside of the contact length. All this has the favorable result that the permissible tolerances as regards the diameters of the shaft opening and the output shaft can increase by a few tens of micrometers. Naturally this lowers costs, inter alia, because it is possible to manufacture the central element and the driving member from materials that are themselves cheaper and are cheaper to process.
A very advantageous turntable is obtained if the contact portion comprises at least a first part and a second part and more preferably exclusively a first part and a second part respectively situated near both end portions of the shaft opening. It has been found that such a contact portion can provide sufficient stability at the clamping connection between the output shaft and the central element, and leads to optimum perpendicularity between the output shaft and the support surface.
It has also been found to be advantageous if the contact length is less than 6 mm, or more preferably less than 4 mm of the insertion length. In this manner, in the case of current shaft diameters for turntables, that are between 1 mm and 10 mm, the friction and displacement forces between the output shaft and the shaft opening during pressing the shaft into the central opening, which forces could lead to the deformations described, remain limited.
The creation of the smaller contact length in relation to the insertion length can take place in accordance with a preferred embodiment form in that the output shaft has a diameter, over a portion of the insertion length that does not coincide with the contact portion, that is smaller than a diameter of the shaft at the location of the contact portion. Alternatively, it is also possible that the diameter of the shaft opening, over a portion of the insertion length that does not coincide with the contact portion is greater than a diameter of the shaft opening at the location of the contact portion. Such a configuration offers production-technical advantages because for the production of the central element using an injection molding process only a limited, once-only adaptation of the mould for the central element is required. The output shaft will in general be manufactured from a metal, as a result of which the provision of a portion with a smaller diameter will require an additional machining operation. Naturally a combination is also possible wherein both the output shaft, over a portion of the insertion length that does not coincide with the contact portion, has a diameter that is smaller that the diameter of the shaft at the location of the contact portion, and the shaft opening, over a portion of the insertion length that does not coincide with the contact portion, has a diameter that is greater than the diameter of the shaft opening at the location of the contact portion. By reducing the diameter of the shaft or increasing the diameter of the shaft opening a space is created in a practical manner between the shaft opening and the shaft. In the area of this space there will be no frictional forces between the shaft and the shaft opening, and space is provided for deformations of material.
According to a very advantageous preferred embodiment an adhesive is provided over a portion of the insertion length, that does not coincide with the contact portion, between the shaft and the shaft opening. With such an adhesive a glued joint is created supplementary to the clamping contact between the shaft opening and the shaft. Such a glued joint is particularly useful if in the course of time relaxation of the clamping contact between the shaft and the shaft opening occurs. Such a relaxation occurs in particular if the central element is manufactured by means of an injection molding process from synthetic material.